Some of the units from which a network is composed are essentially passive in the sense that they are intended merely to pass on or distribute without discrimination packets that they receive Other units, particularly bridges and routers, are more complex devices and commonly include management agents by means of which control over the data packets passing through the switch may be exercised
In recent years many developments have occurred in the implementation of packet based networks and in particular in networks conforming to the ‘Ethernet’ Standards For example, the permitted maximum speeds of communication which can be achieved have increased and standards are now in existence which permit communications to occur at a variety of different speeds Devices are available which are capable of operating at a multiplicity of different rates, such as for example 10 or 100 or 1000 Mbps selectively It is known to provide on network units ports, and associated media access control devices (MACs) which are selectively controllable to operate at any one of a variety of different speeds so that a user may take advantage of a multiplicity of different operating capabilities
Nevertheless, it is for a variety of reasons desirable to be able to restrict arbitrarily the bandwidth available to a user to some figure less than the rate or selected rate at which a communication link could operate For example, many network administrators do not desire their users to have access to high speed networks because allowing such access may dramatically increase the load on existing file servers, routers and wide area network links These reasons may be sufficient to prevent network administrators from installing multiple speed switches
It is therefore generally desirable to provide a feature that can put an upper limit on the bandwidth permitted at an individual port of a switch For example, a network administrator may install a switch that is capable at individual ports of operation at a multiplicity of different rates, such as 10 Mbps and 100 Mbps, but configure the switch such that certain ports are limited to an actual throughput of (for example) 6 Mbps and other ports are limited to 20 Mbps